How can encapsulation be implemented in JavaScript using closures?

Encapsulation in JavaScript can be implemented using closures, creating private variables and methods inside a function that are inaccessible from outside but can be used by functions declared within.

function createCounter() {
  let count = 0; // Private variable

  return {
    increment: function() { // Public method
      count++;
      console.log(count);
    },
    decrement: function() { // Public method
      count--;
      console.log(count);
    },
    getCount: function() { // Public method
      return count;
    }
  };
}

const counter = createCounter();
counter.increment(); // Output: 1
counter.increment(); // Output: 2
console.log(counter.getCount()); // Output: 2
// console.log(counter.count); // undefined - access to private variable is forbidden

In this example:

• count is a private variable accessible only to functions declared inside createCounter.
• The object returned by the function contains public methods (increment, decrement, getCount) that have access to the private variable count thanks to closure.
• From outside, we can only call these public methods on counter, but cannot directly access or modify count.

This allows hiding the internal state of the object and providing a controlled interface for interaction.